1. Field of the Invention
The present invention relates to a reflection type projector adopting a sheet type polarization beam splitter, and more particularly, to a reflection type projector having an improved structure so that aberration of a sheet type polarization beam splitter is corrected.
2. Description of the Related Art
In general, reflection type projection devices are for providing an image by projecting an image generated by a display device using an additional light source onto a screen. Referring to FIG. 1, a conventional reflection type projector includes a light source 10, an optical device 20 for making the light emitted from the light source 10 a uniform and parallel light beam, a cubic polarization beam splitter (PBS) 30 for changing the proceeding path of an input light by transmitting or reflecting the light according to polarization, a reflection type display device 40 for generating an image from a polarized input light input via the cubic PBS 30, and a projection lens unit 50 for magnifying and projecting the light generated from the display device 40 and input through the cubic PBS 30.
The light source 10 includes a lamp 11 for generating light and a reflection mirror 13 for reflecting the light emitted from the lamp 11 and guiding the proceeding path of the light. The optical device 20 includes a glass rod 21 for illuminating a uniform light and a focus lens 23 and a collimating lens 25 for focusing the input diverging light and converting the focused light to a parallel beam.
The cubic PBS 30 includes a mirror surface 31 for reflecting S-polarization light and transmitting P-polarization light of the input light. That is, the S-polarization light of the light emitted from the light source 10 is reflected toward the display device 40 and the P-polarization light is transmitted. Thus, only the S-polarization light of the input light from the light source 10 is used as effective light. Each pixel of the display device 40 is driven independently to selectively polarization-modulate the input light according to a video signal. The light reflected by the display 40 is again input to the cubic beam splitter 30 and the re-input light transmits the cubic PBS 30 in a light amount varying according to the degree of polarization-modulation to P-polarization light to form an image corresponding to the video signal. The projection lens unit 50 magnifies and projects the image transmitting through the cubic PBS 30 on a screen.
In the reflection type projector having the above structure, as the light transmitting through the cubic PBS 30 is symmetrical with respect to an optical axis, a symmetric optical system can be configured. However, in view of the present technical level, the cubic PBS 30 has a lower allowable input angle with respect to the input light than a sheet type PBS. Thus, when the cubic PBS is used, the efficiency of light use is lowered due to the lower allowable input angle.
To increase the efficiency of light use in the cubic PBS approximate to the sheet type PBS, an optical device for emitting collimating light exhibiting low diverging angle and focusing angle is needed. In this case, the light source should be greater in size, which is a disadvantage in configuring a compact optical system.
Also, in the case in which the sheet type PBS is adopted to change the proceeding path of light, the configuration of the light source and the optical device is made easy due to a large allowable input angle, while aberration occurs so that the light transmitted through the sheet type PBS deviates from the optical axis.
To solve the above problems, it is an objective of the present invention to provide a reflection type projector adopting a sheet type PBS to increase the allowable input angle and having an improved structure so that aberration of the sheet type PBS can be corrected.
Accordingly, to achieve the above objective, there is provided a reflection type projector which comprises a light source, a sheet type PBS arranged to be inclined with respect to an optical axis on a proceeding path of light emitted from the light source, a reflection type display mechanism which generates an image from an incident light polarized in one direction passing through the sheet type PBS and reflects the generated image toward the sheet type PBS, a relay lens unit arranged on an optical path for guiding an incident light by focusing and/or diverging the incident light, a mechanism for correcting aberration of an incident light, arranged on a proceeding path of the light generated from the reflection type display mechanism and passing through the sheet type PBS, and a projection lens unit for magnifying and projecting the light transmitted through the correction mechanism toward a screen.
To achieve another aspect of the above object, there is provided a reflection type projector which comprises a light source, an illumination unit for converting light emitted from the light source to a uniform light, a relay lens unit arranged on an optical path for guiding an incident light by focusing and/or diverging the incident light, a device for branching the light polarized in one direction transmitted through the polarization converter according to a wavelength range thereof, a sheet type PBS arranged on a proceeding path of each of the lights branched by the light branching mechanism for converting a proceeding path of the light according to the direction of polarization of an incident light, a reflection type display mechanism which generates an image from an incident light polarized in one direction passing through the sheet type PBS, a color prism for selectively transmitting or reflecting an incident light generated from the reflection type display machanism and passing through the sheet type PBS according to a wavelength thereof, an aberration correcting mechanism for correcting aberration of an incident light, arranged on a proceeding path of the light generated from the reflection type display mechanism and passing through the sheet type PBS, and a projection lens unit for magnifying and projecting light input from the color prism toward a screen.